Regulation Of Anisotropic Cell Expansion By Phosphorylation Of S211 And T212 Residues Of Cellulose Synthase CESA3 In Arabidopsis

Cellulose is a major component in cell wall and carries out many important physiological functions.A large number of researches have shown that there are many crosslink and interaction between light and phytohormone singling pathways.The light can regulate plant morphogenesis via affecting the synthesis and signaling transduction of phytohormone.The study of Herman Hofte's lab indicated that phytochrome B signaling activates the phosphorylation of the cellulose synthase CESA5 and thus regulates anisotropic expansion of hypocotyl cells.Our research focuses on two of the key phosphorylation sites,i.e.,S211 and T212 of Arabidopsis CESA3 to examine the interplay between CESA3 phosphorylation,brassinolide and light signaling on the regulation of anisotropic cell expansion as well as cellulose synthesis and deposition.The main results we obtained are as follows:1.Mutations of S211 and T212 residues of CESA3 to alanine or glutamate have pivotaleffects on regulating the morphogenesis of different tissues,including diffusively growinghypocotyls or primary roots as well as tip-growing root hairs and the observed effects aretissue-specific.For instance,while T212 E mutation had no significant effects on rootelongation,it reduced the lengths of root hairs compared with wild type controls.2.The growth of hypocotyls of S211 A,S211E,T212 A,and T212 E mutants responded differentially in response to the treatment of red and far-red lights,compared with wild type controls,indicating that different light signaling pathways may directly or indirectly affect phosphorylation states of CESA3.In particular,PhyB-mediated red light pathway and PhyA-mediated far red light pathway may have different effects on the phosphorylation states of CESA3,leading to the observed different effects of light signals on anisotropic expansion of hypocotyl cells of the mutants.3.When the mutant lines of S211 A,S211E,T212 A and T212 E were grown on the plates containing EBL,the growth of hypocotyls of the mutants also responded differentially in response to EBL,compared with wild type controls,indicating that phosphorylation of S211 and T212 residues in CESA3 may act downstream of brassinosteroid signaling pathways to regulate the growth of hypocotyls.